Every April, rocket-shaped, yellow, nine-inch reproductive shoots of field horsetail (Equisetum arvense), tipped with small cones, erupt through this patch of waste ground beside Mill Road car park on the bank of the river Tyne. They’ll soon wither, after they’ve released their payload of spores. Then forests of green, corrugated stems and whorls of thread-like leaves, shaped like miniature Christmas trees, will rise from their creeping underground stems.
It’s a prehistoric scene that could have been repeated annually since the Carboniferous period, a living reminder of geological events that produced coal, once the mainstay of the local economy.
Equisetum is considered to be the most durable plant genus, a survivor of extreme climatic events with an evolutionary history stretching back 300m years, to tropical swamps where its ancestors reached tree-like proportions. Its stems accumulate silica and decay slowly, leaving exquisite fossils.
Coal trimmers who, until 50 years ago, loaded holds of colliers a mile upriver from here at Dunston Staiths, shipping 140,000 tonnes of coal each week in the early 20th century, would have had no trouble in matching fossil imprints in their cargo with today’s plants on the quayside.
The plant’s tenacious underground stems, almost impossible to eradicate and so infuriating to gardeners, must be one reason why horsetails have survived so long. But when I took a fertile shoot home to examine under a microscope, another became obvious.
Overnight, the cone released thousands of spores, each about a 20th of a millimetre in diameter. I scraped some on to a microscope slide and, magnified 400 times, could see that each had four arms wrapped around it. These slender structures, freed at last from confinement and experiencing dry air for the first time, uncoiled into long threads, appropriately called elaters, providing aerial buoyancy to carry their spore away on a gust of wind.
The genus Equisetum has already weathered three great mass extinctions that wiped out vast swathes of life on Earth; now, burning coal from those Carboniferous swamps has contributed to climate change and it may be on the threshold of another. But it’s well prepared, with tough subterranean stems and billions of airborne spores that will surely always find safe landfall somewhere.
